Feature/wrapper scripts
Implement the SCRIPT option of the macros.
All wrapper scripts shall be placed in ./python/wrapper/* - I think its a good idea to split our normal python modules from wrapper scripts.
If SCRIPT is not given, it defaults to ./python/wrapper/call_executable.py, which is a simple no-op wrapper. Note however, that inifile dependant stuff can be injected here - as implemented for __ini_optionkey.